1. Field of the Invention
The present invention relates to the field of integrated circuits. Specifically, the present invention relates to an integrated circuit, such as a microprocessor, which may identify its operating characteristics in order to configure a system employing the circuit.
2. Background Information
It is increasingly a requirement in the design of modern integrated circuits to identify certain operating characteristics of those circuits. As manufacturers produce more and more products, even though such products may be plug-compatible with earlier versions of the products, newer versions of these products may include features which may not have been available in earlier versions. For example, until recently, it has not been feasible to implement certain integrated circuits, such as processors, almost entirely in static logic devices. Most prior art processors have been comprised, for the most part, of dynamic logic devices. In contrast to dynamic logic devices, static logic devices have the capability to retain valid data even after a system clock timing reference has been removed or deactivated. Newer processors using exclusively static logic devices, although plug-compatible (they have the same number of pins and are otherwise functionally compatible) with prior version processors using dynamic logic devices, have no way of informing system software or other components in the system of this additional capability. Thus, power management functions in the basic input/output operating system (BIOS) cannot determine whether it should use a power management function which implements a system clock shutdown or whether it should implement a power management function which slows the system clock to a minimum frequency to allow the circuit to retain valid data. Thus, alternative configurations of a system may be desired depending upon certain parts, such as processors, peripheral components, or other integrated circuits in the computer system, depending upon their identified characteristics.
Other characteristics which have been implemented in newer-generation integrated circuits include features which allow such integrated circuits to operate at lower voltages, those that provide an internal clock rate of twice that of the system clock, and other features which are not normally apparent to system software. Therefore, a means is required which allows an integrated circuit such as a processor to communicate its characteristic information to other integrated circuits, such as a main central processor of a computer system.
In prior art computer systems, characteristic information about the parts in the system must be known by the system installer so that he can configure the system appropriately through software or hardware switch settings. It would be desirable to provide such information directly to a main CPU during an appropriate interval, such as power-up initialization or system bootstrap. There is, thus, a requirement that integrated circuits such as microprocessors provide identifying characteristic information, such as the type of logic devices they are comprised of, to allow computer systems and related software to be automatically configured.